A high-speed serial interface or high-speed serial link (HSSL), as described in DE 10 2013 004 542 A1, makes it possible to connect a microcontroller and a remote station, such as, for instance, another microcontroller or a less powerful modular unit such as an ASIC (application specific integrated circuit) using a small number of lines and nevertheless achieve a high data rate.
This interface is conceived as a bidirectional point-to-point connection, with both users able to transmit messages at any time. Each message is acknowledged with a confirmation signal—a positive-acknowledgement signal—or a non-confirmation signal—a negative-acknowledgement signal. Transmission can take place on various prioritizable logical channels. Longer messages are split into several message packets. As a result, it is possible to interrupt longer low-priority messages and to embed higher-priority messages. By virtue of the logical channels, it is also possible to assign the positive-acknowledgement and negative-acknowledgement signals to a message. The protocol allows the transmission of an address, so that writing can take place from the transmitter directly into memory areas of the receiver. The electrical protocol allows, in addition, the outputs of an individual bus user to be switched to high impedance.
By virtue of the point-to-point connection which is merely provided, only one remote station—in engine control units, typically a user-specific modular unit (ASIC)—is able to communicate with the microcontroller. This is not always of practical use; for reasons of system partitioning it would be advantageous to be able to operate also several ASICs at this interface. However, the difficulty in this case lies in the fact that the microcontrollers are already available and the interface specification cannot be changed.